The present invention relates to a high voltage switch, and, more particularly, to a high voltage switch for use in a double-coil ignition system.
The invention is based on an ignition system e.g. as is known from DE-OS 37 31 393. High-voltage switches which are arranged on the secondary side, preferably in the spark plug terminal, are used in the above-mentioned ignition system. State-charging or breakdown diode cascades are used as high-voltage switching elements. Ten to fifty diodes are stacked one on top of the other depending on the electric strength of an individual diode and depending on the desired breakdown voltage. This kind of high-voltage switch which changes suddenly from the blocking state to the conducting state makes it possible to eliminate the influences of shunts at the spark plug. Because of their self-capacitance, long ignition lines following the breakdown diode have disadvantageous effects on the steepening effect of the breakdown diode. For this reason the high-voltage switch is preferably arranged in the spark plug terminal. When such semiconductor switching elements are used with double ignition coils, the breakdown voltage must be kept low enough so that it is achieved in every case because of the division of voltage on the secondary side. However, this has the disadvantage that there is hardly any steepening effect when the breakdown voltage clearly lies below 11 kV.
The present solution endeavors to find a favorable size of the breakdown voltage with respect to the greatest possible steepening effect for optimum use of the high-voltage switch.